This invention relates generally to a plug including a plug body having an axial bore for insertion of a cable at one end of the plug body for connection to electric contact elements arranged at the other end of the plug body, and more particularly to a plug including a strain relief mechanism located at the first end of the plug body and having at least two clamping elements adjustably supported for clamping the cable.
In a prior plug, a strain relief mechanism is formed by three annular clamping segments that are joined by screws. When the screws are tightened, an area through which the cable passes is reduced. The annular segments are movably supported on an end of the plug body, and are covered by a cover screwed onto the plug body when the plug is assembled. An o-ring is arranged between the cover and the annular segments. When the cover is screwed on to the plug body, the o-ring is compressed and pressed in the direction of the cable to seal the cable. The cable extends through an axial bore in the plug body up to the contact elements to which it is connected.
The strain relief mechanism can be fitted to cables of different diameters in a simple manner and safely prevents a direct tensile load on the connection between the cable and the electric contact elements.
In one general aspect, the invention features a plug including a plug body with an axial bore. A cable may be inserted into the plug body at the first end of the plug body and may be connected to contact elements arranged at the second end. A strain relief mechanism positioned at the first end of the plug body has at least two clamping elements adjustably supported for clamping the cable. The plug body includes at least two sliding guides open towards the axial bore and towards the outside, with the clamping elements being movably guided in the sliding guides.
Use of the sliding guides provides a plug that tends to be even simpler and less expensive than known plugs, while also providing improved accessibility to the strain relief mechanism. Through use of the sliding guides, the clamping elements are directly supported in the plug body and not at one of its ends. Furthermore, since the clamping elements are accessible through the sliding guides, which are open to the outside, they can be adjusted for clamping the cable. The sliding guides can be formed in a simple and inexpensive manner as radially inwardly extending openings provided in a wall of the plug body. Side walls of these openings may serve for guiding the clamping elements. The sliding guides permit a highly efficient strain relief mechanism that provides safe clamping of cables having different diameters.
The plug body includes at least one plug inset provided with the contact elements, a plug cap, and a plug sleeve arranged between the plug inset and the plug cap. At least the plug cap and the plug sleeve can be rotated with respect to one another. To realize simple accessibility to the strain relief mechanism, the sliding guides can be formed directly in the plug cap.
To secure the cable against tension directly after insertion, the sliding guides may be arranged adjacent to an insertion opening of the first end of the plug cap. To permit secure coupling to cables having different diameters, the sliding guides may be in the form of longitudinal holes extending transversely to the axial bore beyond the insertion opening, and the clamping elements may have shapes complementary to the longitudinal holes. In this manner, the clamping elements are guided on all sides in the longitudinal holes.
In one implementation, each clamping element has substantially planar side faces extending transversely to the axial bores and end curves connecting the ends of the side faces. This leads to an approximately elongate, oval cross-section for a clamping element of this kind.
Each clamping element may include a protruding edge extending transversely to the cable on a lower side of the clamping element pointing to the cable. When the clamping element approaches a cable, this protruding edge is pressed into the cable""s insulation. The cable may be held on both sides by the use of two opposite clamping elements to secure against tension on the contact elements. To enlarge the surface contact between the clamping element and the cable or the cable""s insulation, the lower side of the clamping element facing the axial bore may have a concave recess for at least partially accommodating the cable. Since the cables usually have a circular cross section, the recess can also be substantially circular.
The recess may have at least one clamping projection protruding in the direction of the cable on the clamping side facing the cable. When the clamping elements are tightened, this clamping projection is pressed partially in to the insulation of the cable. In one implementation, the clamping projection can be formed as a clamping rail extending in the axial direction. The clamping rail serves both to support the cable and to reduce rotation of the cable.
To prevent a clamping element from falling out of a sliding guide when releasing the clamping elements from one another, at least one clamping element may have an abutment projecting from the clamping side in the axial direction over a side face to the outside. The abutment contacts the insertion opening, such that the clamping element only moves radially to the outside until the abutment contacts the inner rim of the insertion opening. Each of the clamping elements may have such an abutment. The abutments may be arranged such that the insertion opening is fully open when the abutments contact the inner rim of the insertion opening. In some implementations, at least one of the clamping elements may be removable from the clamping element""s sliding guide.
To improve movement of the clamping elements in the sliding guides, a guiding projection may project toward the outside from at least one side face of a clamping element. The guiding projection movably engages a corresponding guide groove which extends in the displacement direction of the clamping element.
The appearance of the plug may be improved and a possible risk of injury may be avoided by forming an outer side of the clamping element opposite to the lower side to have a radius of curvature substantially equal to the outer side of the plug cap. In this way, the clamping elements do not protrude with sharp edges, and, instead, are arranged in the sliding guides, depending on the diameter of the cable to be secured, in a flush or countersunk manner.
Although the cable is held partially secure against rotation, as stated above, a rotation of the cable relative to the electric contact elements may, however, still take place if, for example, the plug cap is twisted relative to the plug body. This can be prevented through use of a rotation prevention projection that extends from at least one clamping element substantially in the axial direction. The projection engages in different rotational positions of the plug cap relative to the plug sleeve through interaction with engagement recesses formed in the plug sleeve. By the mutual engagement of the rotation preventing projection and the engagement recess, a further rotation of the plug cap relative to the plug sleeve or an accidental release of both members is prevented.
In one implementation, the engagement recess is formed between walls extending radially outward relative to the axial bore. The walls restrict the rotation of the plug cap relative to the plug sleeve in that the rotation prevention projection abuts one of the walls in the direction of rotation.
To enable multiple relative positions between the plug cap and the plug sleeve, and at the same time to maintain the protection against rotation, multiple engagement recesses can be arranged equidistantly around the circumference of the plug sleeve.
To easily connect the plug sleeve and the plug cap, the plug sleeve may include an end section at least partially provided with an external thread, with the plug cap having an internal thread section being screwable onto the end section. To form the rotation prevention projections in a simple manner and with a short length, the engagement recesses of the plug sleeve can be arranged directly adjoining the end section.
To cover the recesses when screwing the plug cap onto the plug sleeve, the plug cap may have an annular flange at least accommodating the recesses and following the internal thread section.
To permit simple access to the rotation prevention projection from the outside, the insertion opening may be arranged in the annular flange through which the rotation prevention projection can be engaged with a recess. For releasing the plug cap, the rotation prevention projection can be disengaged from the recess through the insertion opening from the outside so that a subsequent rotation of the plug cap relative to the plug sleeve can be performed. Thus, both the rotation prevention projection and the clamping elements can be adjusted from the outside for holding or releasing the cable.
In some implementations, when the walls restricting the engagement recesses extend radially beyond the external thread of the end section, the annular flange is formed with an external diameter greater than an external diameter of the internal thread section.
The rotation prevention projection may be implemented in different ways. For example, a rotation prevention projection that is simple to manufacture projects in an arm-like manner from a clamping element and has a free end that engages through the insertion opening into a recess with clamping elements attached to one another. A rotation prevention projection or rotation prevention arm may be formed at each clamping element.
A rotation prevention arm may extend in a first arm section adjacent to the clamping element transversely to the outside relative to the plug cap and in a second arm section connected thereto transversely downward in the direction of the axial bore, such that an obtuse angle is formed between the two arm sections. The second arm section projects through the insertion opening into the interior of the plug cap and engages the engagement recess.
The internal thread section on an outer side may have a ramp recess substantially extending in the direction toward the first arm section. The first arm section with clamping elements attached to one another can be inserted at least partially into this ramp recess, such that the rotation prevention arm projects less over the outer side of the plug cap toward the outside.
A simple possibility for the mutual adjustability of the clamping elements and for fixing them to each other is when the clamping elements have bores at their lateral ends for accommodating attachment and adjustment screws. The screws may be partially screwed into the clamping element with the rotation prevention arm, and they may be inserted into the corresponding sliding guide. The other clamping element in its sliding guide is secured against falling out by the abutment noted above. By further turning the screws, the two clamping elements can be fixed to one another and can be moved toward one another for clamping the cable passed between them.
To arrange the screws in a manner sunk in the clamping elements with clamping elements fixed to one another, each bore may have (at least in the clamping element from where the screws are inserted) an accommodation bore section open toward the outside and having an enlarged diameter for accommodating a screw head.
To facilitate screwing the plug cap on to the plug sleeve and to facilitate a mutual release, the internal thread section can be formed at least adjacent to the annular flange as a screw aid with a hexagonal outer contour. A wrench or the like can then be used as an aid for twisting the screw cap.
To restrict a movement of each clamping element within the sliding guide in the direction toward the other clamping element, abutment projections located approximately centrally with respect to the insertion opening can radially project inwardly within the sliding guide. Ends of the lower sides of the respective clamping elements can be abutted against the abutment projections.
To ensure that the clamping elements can be positioned close enough to one another to clamp a cable with a small diameter, an end recess can be arranged at the end of the lower side to at least partially receive the accommodation projection.
When using the plug in environments in which there is a risk of explosion, a sealing element for sealing the electric connection between the cable and the electric contact elements within the plug must be provided. Such a sealing element is described, for example, in U.S. Pat. No. 5,167,527, which is incorporated by reference. The sealing element is held between two annular elements and is compressed and sealed against the cable when the annular elements are moved toward one another by screwing the cover onto the plug body.
A sealing seat for accommodating a sealing element can be connected at the free end of the end section of the plug sleeve at the external thread. In this manner, the sealing seat is not a separate component, but, instead, is part of the plug sleeve. The sealing seat may be formed by an opening rim of the axial bore in the end section at which the substantially annular sealing element abuts with an abutment end. When screwing on the plug cap, the sealing element may be pressed against the outer side of the cable for sealing.
To hold the sealing element in a more secure manner, in particular when assembling or disassembling the plug, an annular chamber for accommodating the sealing element may project from the opening rim in the direction toward the plug cap. The annular chamber has a varying diameter, and the sealing element is held in the annular chamber and secured against accidentally falling out.
A taper may be formed within the plug cap to enable simple variation of the diameter of the annular chamber and thereby a pressing of the sealing element to an outer side of the cable for sealing purposes. When the plug cap is screwed on to the plug sleeve, the taper contacts the annular chamber for the purpose of reducing its diameter. The taper may be implemented as a section that gradually reduces in diameter within the axial bore of the plug cap. When screwing the plug cap on to the plug sleeve, the annular chamber in the corresponding section is gradually compressed by this internal diameter reduction and the sealing element is pressed against the cable.
The annular chamber may have a wall of resiliently deflectable lamellae, which project from the opening rim substantially in the axial direction. The free ends of the lamellae then contact the section of reducing internal diameter when screwing on the plug cap and are pressed radially inwards.
To hold the sealing element and at the same time to facilitate a screwing on of the plug cap, the lamellae may obliquely extend from the opening rim to the inside. It is also possible that the lamellae may have an inclination only on their radially outward side at least at the free end.
To further improve the sealing between the plug sleeve and the cable provided by the sealing element, the opening rim may have a sealing lip protruding in the direction toward the abutment end of the sealing element. For example, the sealing lip may be formed as a V-notch encompassing the axial bore within the plug sleeve. The sealing element may have a sealing rim engaging into a recess between the V-notch or sealing lip and lamellae, respectively.
To enable a simple, inexpensive adaptation to different diameters of cables without completely exchanging the sealing element, the sealing element may at least be formed of two parts, an outer sealing ring and an inner sealing ring. The outer sealing ring can be used independent of the cable used while the inner sealing ring is exchangeable for adaptation to different diameters. To this end, the inner sealing ring may have an annularly extending sealing flange as a sealing rim, which, as stated above, engages into the recess between the V-notch or sealing lip and lamellae, respectively. The sealing flange may project radially outwardly to such an extent that the outer sealing ring can be slipped on to the inner sealing ring until the outer sealing ring abuts the sealing flange at an end of the inner sealing ring.
To reduce costs, the outer sealing ring and the inner sealing ring may be made of different materials. For example, the outer sealing ring may be made of a less expensive material which only takes over a minor part of the sealing function, while the inner sealing ring with the rotating sealing flange serves for the actual sealing and may be made of a more expensive material which safely seals the cable with respect to the plug body.
The rotation prevention projection and the rotation prevention arm may be resiliently deflectable so that, when the clamping elements are not released from one another or only released from another to a small extent, a relative rotation between the plug cap and the plug sleeve is possible by deflecting the rotation prevention arm to the outside.
The strain relief and the rotation prevention can be established substantially independent of one another. Independent of the position of the insertion opening with respect to the engagement recess, the strain relief can be established through the strain relief mechanism. The rotation prevention is also established after establishment of the strain relief by engagement of the free arm end by the insertion opening into an engagement recess.
The plug with its various members may be made, for example, from a plastic material, such as glass-fiber reinforced polyester or polyamide.
Other features and advantages will be apparent from the description and drawings, and from the claims.